1. Field of the Invention
This invention relates generally to radial lip seals, and more particularly, to radial lip seals which can accommodate significant shaft deflection in an environment in which the shaft rotates at low speed, and under high torque conditions and in which the fluid being sealed attains high pressures.
2. Background Art
Lip seals are usually molded of a resilient elastomeric or polymeric material. They are secured in fluid tight relation to a housing and surround a rotating shaft which extends through an aperture in the housing wall. The sealing lip is in sealing relationship to the shaft to contain the fluid in the housing.
Lip seals components or elements include a rigid case or retainer to add rigidity and to unitize the seal assembly. The case also aids in the installation, withdrawal and retention of the seal relative to the housing. The resilient body includes a secondary seal to seal against the housing and one or more resilient sealing lips which are maintained in sealing contact with the shaft.
Lip seals experience a wide variety of uses in which operating temperature and pressure conditions, expected shaft speeds, and the make-up of the medium to be contained dictate the requirements of a particular construction. Typically, however, the rigid component or retainer is formed of hard plastic, such as phenolic, steel or stainless steel and the resilient lips are defined by elastomeric or polymeric members such as molded rubber, polytetrafluroethylene or other known materials. The resilient element may be molded as a single body or may comprise a plurality of separate elements connected together in fluid tight relation.
The nature of lip seal applications expose the seal to conditions of significant shaft movement relative to the surrounding housing. Shaft deflection relative to either the housing or the bore results in a wobble of the shaft during rotation of the shaft, also referred to as shaft run-out. A significant degree of shaft run-out often challenges the effectiveness of the lip seal.
Specific applications for lip seals may include automotive, appliance and industrial applications. Certain applications subject lip seals to extreme service conditions such as in air conditioning compressors, where the shaft is typically driven by a belt and pulley through an electric clutch, and in oil pumps which generally pressurize oil to high pressures, to thereby permit effective circulation of the oil through the engine and oil filter. Compressor and oil pump design typically results in shaft wobble, bending distortion and misalignment of the shaft axis relative to the housing aperture. Ideally, the lip seal assembly takes into account the established tolerances of the devices in which the lip seal is used in order to minimize the associated manufacturing costs.
Efforts to provide a lip seal to accommodate shaft run-out or misalignment include use of extended conical shapes, multiple lips and other variations and alterations of the resilient element. An effective arrangement is disclosed in U.S. Pat. No. 5,503,408, issued Apr. 2, 1996, and commonly assigned with this invention to John Crane Inc., Morton Grove, Ill. The seal disclosed and claimed in U.S. Pat. No. 5,503,408 embodies multiple resilient lips which provide for an auxiliary or alignment lip interposed between the shaft and the sealing lip for centering the lip seal. Under conditions of misalignment, the auxiliary lip contacts the underside of the primary sealing lip and causes a displacement of that lip in the direction of displacement of the shaft relative to the center of its associated housing bore. Displacement of the auxiliary lip causes the primary sealing lip to "follow" the shaft and, thereby, maintain the integrity of its sealing relation to the shaft. The lip seal described in U.S. Pat. No. 5,503,408 is used in relatively low pressure type applications.
The misalignment problem is also addressed in commonly assigned copending U.S. patent application Ser. No. 08/606,421, filed on Feb. 23, 1996, entitled "Improved Radial Lip Seal" and having at least one common inventor with this invention. The features of that invention include a sleeve bearing member which defines an annular body having a "T-shaped" cross section. An outer cylindrical surface of the annular body is sized to coincide with the inner axial surface central of an axial wall of an associated retainer. A radial edge of the annular body is in contact with the inner surface of an axial wall of the retainer so as to secure the bearing member in the assembly and retain it against rotation and radial displacement. A radial inner portion of the bearing member defines a cylindrical sealing surface sized to be in close supporting contact with the outer surface of the shaft. When installed in a housing, the sealing elements of the seal assembly are disposed inboard of the bearing member, thereby maintaining the bearing outward of the sealed chamber in the environment external to the housing. The bearing disclosed in the patent, which is interposed between the lip seal and the fluid being sealed within the housing, also acts to maintain orientation and position of the lip seal.
The bearing member disclosed in aforementioned U.S. patent application Ser. No. 08/606,421 may be either rigidly or resiliently mounted on, and in contact with, the outer diameter surface of a supporting retainer to provide shaft vibration dampening. In the case of a resilient mounting, the bearing member includes a radial wall in frictional engagement with the resilient body supporting the bearing member to restrict rotation of the bearing member relative to the housing.
All of the prior efforts which provide lip seal centering by means of a 0 bearing member work adequately in the low pressure environments for which they are intended. However, in the event that the fluid being sealed attains high pressures, the lip seal becomes subject to deformation from axially directed pressure forces, resulting from the high pressures acting on the radial area of the lip seal, which press the radial sealing lip against the bearing. At high pressures, the radial seal lip is further subject to folding over at the shaft, thereby resulting in a loss of sealing capacity.
To some extent, bearing members which are utilized in the efforts and examples described above maintain seal lip centering and also contain the seal lip in the desired orientation and position between the bearing and the high pressure fluid being sealed. However, bearings, by the nature of their construction and function, extend from the seal lip and provide rigid axial support to the retainer member relative to the shaft. In most instances, the outer diameter of the bearing is flush against the inner diameter of the rigid retainer member, so that any shaft deflection causes the bearing to impart that deflection to the retainer, thereby maintaining a predetermined relative orientation between the lip seal and the rotating shaft. Dampening action of a resilient mounting between the bearing and the retainer member absorbs the majority of the deflection. However, even in the resilient mounting example, the abutment of the bearing member with the resilient retainer subjects the bearing to continual repeated stress, which over extended periods of time can cause the deterioration and destruction of the bearing.
The present invention addresses the needs of the seals in some applications to accommodate a greater amount of pressure and inflexibility which results from the increased pressure sealed fluid environments. The ability of the improved lip seal according to the present invention to accommodate great pressures allows for the elimination of expensive case pressure drain systems that are presently required for high pressure applications.